No. There would be no way to get it back after restarting, unless you trade it to another gen5 game beforehand to later trade it back to your white game. If you own any newer games you could send it there instead if you wanted, with Poké Transporter+Pokémon Bank. Though, since you have an Action Replay device, you could try using it to reactivate the event if it has a trustworthy code for that.
I hope this helps!